1. Field of the Invention
The present invention relates to a blood pump and a ventricular assist device. More particularly, the invention relates to a blood pump and a ventricular assist device capable of effectively suppressing the development of thrombi.
2. Related Art
Blood pumps for assisting the circulation that are used in case of cardiogenic shocks or acute myocardial infarction during or after open heart surgery need to operate continuously for the period required for the patient""s cardiac function to recover.
Pulsatile type blood pumps are widely used for assisting the circulation. However, the pulsatile type blood pumps have a insufficient long term reliability, as a result of the polymer used for materials of the pulsatile type blood pumps. Non-pulsatile blood pumps, such as Rotaly blood pumps, made of metal have a long term reliability compared to pulsatile type blood pumps. However, there exist a demand or need to improve thrombus suppression function. Coagulation factors in the blood such as thrombocytes are activated as a result of blood in contact with foreign materials, and thrombus formation has some effects of performance of the blood pumps.
To fulfill this demand, Japanese laid-open application JPH7-116245A discloses an invention that consists in coating all blood pump parts in contact with blood with a hemocompatible material, such as antithrombogenic material, made of a phospholipid polymer.
According to this prior art invention, coagulation factors in the blood such as thrombocytes will not be activated and the development of thrombi will be effectively suppressed, as a result of all parts in contact with blood being coated with a hemocompatible material made of a phospholipid polymer. This enables a blood pump capable of long term continuous operation over two weeks or more.
However, if thrombi develop inside the blood pump during or after open heart surgery, the blood pump might stop operating. Therefore, it has been common practice up to now to administer the patient with an anticoagulant when making use of a blood pump, leading to an increased risk of hemorrhage complications during the postoperative acute phase (a phase or period lasting for about one month after surgery during which there is a high risk of hemorrhage).
An object of the present invention is to solve these problems by providing a blood pump and a ventricular assist device that have a considerably increased thrombus suppression function compared to current blood pumps, in order to allow long term continuous operation of the blood pump even without any administration of anticoagulants to the patient, and thereby enable the suppression of hemorrhage complications during the postoperative acute phase.
The blood pump according to the one aspect of the present invention comprises a casing having a blood inlet and a blood outlet, and an impeller for circulating blood by rotating inside the casing, wherein both the casing""s and the impeller""s surfaces in contact with blood are formed of a biocompatible metal, and onto the surfaces in contact with blood a coating film of a hemocompatible material comprising a phospholipid polymer is formed.
The blood pump according to the present invention effectively suppresses the development of thrombi without activating blood coagulation factors such as thrombocites (blood platelets) in the blood, thanks to a coating film of a hemocompatible material made of a phospholipid polymer being formed onto the surfaces in contact with blood of the casing and the impeller composing the main part of the blood pump.
The blood pump of the present invention furthermore maintains the function of effectively suppressing the development of thrombi without activating blood coagulation factors such as thrombocites (blood platelets) in the blood, even if a part of the coating film of a hemocompatible material made of a phospholipid polymer should for elute or come off with long term continuous operation, as the metal below is a biocompatible metal, that is, the surfaces in contact with blood of the casing and impeller composing the main part of the blood pump are made of a biocompatible metal.
Therefore, the blood pump according to the present invention has a considerably increased thrombus suppression function compared to current blood pumps, thus allowing long term continuous operation of the blood pump even without any administration of anticoagulants to the patient, and as a result, enabling the suppression of hemorrhage complications during the postoperative acute phase.
Furthermore, as the blood pump according to the present invention has a considerably increased thrombus suppression function compared to current blood pumps, thus allowing long term continuous operation for 30 days or more, it can be used well into the postoperative chronic phase (the chronic phase is the phase or period following the acute phase of about one month after the surgery in which the risk of hemorrhage is reduced as compared to the risk during the acute phase).
During the chronic phase, as the threat of hemorrhage complication development decreases, anticoagulant administration in combination with the use of the blood pump becomes a rational choice, thereby assuring even longer term continuous operation.
In this context, xe2x80x9cthe surfaces in contact with blood are formed of a biocompatible metalxe2x80x9d includes both of the following interpretations, either the whole component, or only the parts in proximity of the surfaces are formed of a biocompatible metal.
According to the present invention, a similar advantageous effect can be obtained irrespective of whether the blood pump is of the centrifugal type or of the axial flow type.
The blood pump generally comprises a pump part and a drive part, and among the partition parts to separate the two, the pump side part (also called: pump base part) also belongs to the above-mentioned casing.
The hemocompatible material comprising a phospholipid polymer also includes such ones, wherein not only all units but also only some part of the units include a phospholipid.
In the blood pump according to the present invention, the biocompatible metal preferably is pure titanium or a titanium alloy, the metals being highly suited for living bodies. As a titanium alloy, Ti-6AI-4V alloy (especially ELI (Extra Low Interstitial) glade) with 6% aluminum and 4% Vanadium added to the titanium is preferably used.
In the blood pump according to the present invention, the biocompatible metal preferably is pure titanium.
In the blood pump according to the present invention, the arithmetic mean of the surface roughness Ra of both the casing""s and the impeller""s surfaces in contact with blood preferably is 0.5 xcexcm or less. The arithmetic mean of the surface roughness Ra of the surfaces in contact with blood of 0.5 xcexcm or less leads to a smooth coating of a material suited for blood comprising a phospholipid onto its surface, thereby even more effectively suppressing the development of thrombi as the blood flow will flow smoothly and sedimentation will be prevented. From this point of view, it is more preferable for the arithmetic mean of the surface roughness Ra of both the casing""s and the impeller""s surfaces in contact with blood to be 0.2 xcexcm or less.
In the blood pump according to the present invention, preferably a coating film of a hemocompatible material comprising a phospholipid polymer is also formed onto the parts in contact with blood other than those of the casing and the impeller.
By also forming a coating film of a hemocompatible material comprising a phospholipid polymer onto these other parts in contact with blood, as for example onto a mechanical seal, the suppression function of thrombi development can be further increased.
In the blood pump according to the present invention, the arithmetic mean of the surface roughness Ra of these other surfaces in contact with blood preferably is 0.5 xcexcm or less. The arithmetic mean of the surface roughness Ra of the other surfaces in contact with blood of 0.5 xcexcm or less leads to a smooth coating of a hemocompatible material comprising a phospholipid onto its surface, thereby even more effectively suppressing the development of thrombi as the blood flow will flow smoothly and sedimentation will be prevented. From this point of view, it is more preferable for the arithmetic mean of the surface roughness Ra to be 0.2 xcexcm or less.
In the blood pump according to the present invention, the thickness of the coating film preferably is 0.5 xcexcm or less. A coating film thickness of 0.5 xcexcm or less leads to a smooth coating film, thereby even more effectively suppressing the development of thrombi as the blood flow will flow smoothly and sedimentation will be prevented.
In the blood pump according to the present invention, the impeller preferably is an open vane type impeller. If the impeller is an open vane type impeller the energy exchange efficiency is slightly reduced compared to closed vane type and semi-closed vane type impellers, but the blood flow will get even smoother and unlikely to accumulate. Therefore, the development of thrombi is even more effectively suppressed.
In the blood pump according to the present invention, the hemocompatible material comprising a phospholipid polymer preferably is a (meth)acryloyloxy lower alkylphosphorylcholine copolymer as it is very well suited for contact with blood.
In the blood pump according to the present invention, the (meth)acryloyloxy lower alkylphosphorylcholine copolymer preferably is a copolymer of a (meth)acryloyloxy lower alkylphosphorylcholine and a (meth)acrylic acid ester. Even though a (meth)acryloyloxy lower alkylphosphorylcholine homopolymers would be even better suited for contact with blood, there is a concern as it is highly hydrophilic and therefore easily elutes. By adding a (meth)acrylic acid ester, the extent of hydrophilic properties is adjusted, and while keeping good blood suitability, the coating film is made robust against elution. As a result of experiments it became understood, that xe2x80x9c(meth)acryloyloxy lower alkylphosphorylcholine to (meth)acrylic acid esterxe2x80x9d is preferably around xe2x80x9c30% to 70%xe2x80x9d in adding molar ratio.
In the blood pump according to the present invention, the (meth)acryloyloxy lower alkylphosphorylcholine preferably is a 2-methcryloyloxyethyl-phosphorylcholine having the following formula, for being especially highly suited for blood. 
In the blood pump according to the present invention, the (meth)acrylic acid ester preferably is a butyl methacrylate. This is because the hydrophilic properties are easy to adjust, and the mechanical strength is easy to preserve. Furthermore, butyl methcrylate is desirable whether it be as n-butyl methcrylate or as isobutyl methcrylate.
In the blood pump according to the present invention, the coating film is preferably formed by coating a solution containing a copolymer of the (meth)acryloyloxy lower alkylphosphorylcholine and the (meth)acrylic acid ester onto the surfaces in contact with blood.
The blood pump according to the other aspect of the present invention comprises: a casing having a blood inlet and a blood outlet; and an open vane type impeller for circulating blood by rotating inside the casing, wherein both the casing""s and the impeller""s surfaces in contact with blood are formed of pure titanium, and onto the casing""s and impeller""s and other parts"" surfaces in contact with blood a coating film of a (meth)acryloyloxy lower alkylphosphorylcholine copolymer is formed.
In this way, the blood pump of the present invention""s thrombi development suppression function is further increased compared to current blood pumps, as the surfaces in contact with blood of the main parts of the blood pump are formed of pure titanium, and, in addition to these surfaces in contact with blood for example onto other parts like a mechanical seal""s surface in contact with blood a coating film of a (meth)acryloyloxy lower alkylphosphorylcholine copolymer is formed, and in addition, because the impeller is an open vane type impeller.
The ventricular assist device of the one aspect of the present invention comprises: a blood pump comprising a casing having a blood inlet and a blood outlet; and an impeller for circulating blood by rotating inside the casing, wherein both the casing""s and the impeller""s surfaces in contact with blood are formed of a biocompatible metal, and onto the surfaces in contact with blood a coating film of a hemocompatible material comprising a phospholipid polymer is formed;
an inlet side artificial blood vessel connected to the blood pump;
a cannula connected to the inlet side artificial blood vessel; and
an outlet side artificial blood vessel connected to the blood pump,
wherein the cannula is formed of a biocompatible metal, and onto the cannula""s surfaces in contact with blood a coating film of a hemocompatible material comprising a phospholipid polymer is formed.
Therefore, the ventricular assist device of the one aspect of the present invention, as mentioned above, features a blood pump with a high thrombi development suppression function compared to current blood pumps. Furthermore, in the cannula the thrombi development suppression function has also been increased. Therefore, the ventricular assist device of the present invention is a very outstanding ventricular assist device that effectively prevents the development of thrombi.
The ventricular assist device of the other aspect of the present invention comprises: a blood pump comprising a casing having a blood inlet and a blood outlet, and an open vane type impeller for circulating blood by rotating inside the casing, wherein both the casing""s and the impeller""s surfaces in contact with blood are formed of pure titanium, and onto the casing""s and impeller""s and other parts"" surfaces in contact with blood a coating film of a (meth)acryloyloxy lower alkylphosphorylcholine copolymer is formed;
an inlet side artificial blood vessel connected to the blood pump;
a cannula connected to the inlet side artificial blood vessel; and
an outlet side artificial blood vessel for outlet side use connected to the blood pump,
wherein the cannula is formed of a biocompatible metal, and onto the cannula""s surfaces in contact with blood a coating film of a hemocompatible material comprising a phospholipid polymer is formed.
Therefore, the ventricular assist device of the other aspect of the present invention, as mentioned above, features a blood pump with a high thrombi development suppression function compared to current blood pumps. Furthermore, in the cannula the thrombi development suppression function has also been increased. Therefore, the ventricular assist device of the present invention is a very outstanding ventricular assist device that effectively prevents the development of thrombi.